象山港人工鱼礁区的网采浮游植物群落组成及其与环境因子的关系

根据2010年1月(冬)、4月(春)、7月(夏)和11月(秋)对象山港人工鱼礁区及其邻近海域的网采浮游植物样品,共鉴定出浮游植物8门74属220种,主要由硅藻(168种)和甲藻(38种)组成。春、秋、冬季全区浮游植物丰度(分别为67.85、65.88和56.77×104个/m3)显著高于夏季(7.19×104个/m3),优势种主要有琼氏圆筛藻(Coscinodiscus jonesianus)、大洋角管藻(Cerataulina pelagica)、洛氏角毛藻(Chaetoceros lorenzianus)和罗氏角毛藻(C.lauderi)等,其中琼氏圆筛藻为全年的优势种,且在春、冬季为该海域的绝对优势种。浮游植物群落参数(丰度、chl a浓度、种类数、Shannon-Wiener多样性、Pielou均匀度和Margalef丰富度等指数)和环境因子(温度、盐度、透明度、pH值、DO、悬浮物、DIN、PO4-P和SiO3-Si浓度)均存在极显著的季节变化(P<0.001),但区域(鱼礁区与对照区)间基本无显著差异。聚类、多维尺度和相似性分析结果也表明,浮游植物群落组成存在显著季节差异(P=0.001),但区域间无显著差异。可见,人工鱼礁投放对网采浮游植物群落无显著影响。究其原因:(1)可能是该海域人工鱼礁投放数量不多,仅有230个水泥鱼礁体(共5000空立方),建礁时间也较短,导致其生态效应在短期内难以显著体现;(2)对照区与人工鱼礁区的距离较近,且采样站位均靠近岛屿,潮流和岛屿对浮游植物的影响可能超过了人工鱼礁投放对其的影响。典范对应分析(Canonical correspondence analysis,CCA)显示,影响浮游植物群落的主要因子依次为温度、营养盐、盐度和悬浮物。

Community composition of net-phytoplankton and its relationship with the environmental factors at artificial reef area in Xiangshan Bay

Xiangshan Bay (121°25'-120°00'E, 29°05'-29°46'N), located on the east coast of China, is a long semi-enclosed bay with slow rate of water exchange. As one of the most important economic and aquaculture base in Zhejiang province, Xiangshan Bay has confronted a series of ecological challenge such as the development for coastal power plant, industrial construction, tidal flat reclamation and over-fishing. In order to restore the damage environment of Xiangshan Bay, the local government has begun to settle 230 concrete reefs (a total of 5000 air cubic meters) successively near the Baishi Island since 2008. Most researches so far focused on the artificial reef itself (e.g. body design, settlement area, pavement method and management) and its influence on the water quality, attachment organisms, benthos and fishery resource. However, report about the effects of artificial reef on phytoplankton is rare. Actually, the phytoplankton, as the basic and essential part of food chain, is very important for the ecological assessment and the community of phytoplankton should be taken into consideration of the artificial reef effects on the ecological restoration and fishery resource recovery. This paper represents the seasonal community composition of net-phytoplankton in artificial reef areas and their adjacent waters in Xiangshan Bay. The net-phytoplankton samples were collected in January (winter), April (spring), July (summer) and November (autumn) 2010, and a total of 8 phyla, 74 genera, and 220 species were found, mainly including 168 diatom species and 38 dinoflagellate species, and other rare species such as Cyanophyceae, Chlorophyceae, Euglenophyceae, Chrysophyceae, Cryptophyceae and Xanthophyceae. The phytoplankton abundances in spring, autumn and winter (67.85,65.88 and 56.77×10⁴ Cells/m³, respectively) were significantly higher than those in summer (7.19×10⁴ Cells/m³). Coscinodiscus jonesianus, Cerataulina pelagica, Chaetoceros lorenzianus and C. lauderi were the main dominant species, especially C. jonesianus was the absolute dominant species in spring and winter. Both the phytoplankton community parameters (abundance, chl a concentration, species number, Shannon-Wiener diversity, Pielou evenness and Margalef richness index) and the environmental variables (temperature, salinity, transparency, pH value, DO, suspended solids, DIN, PO₄-P and SiO₃-Si levels) are seasonally different significantly (P < 0.001) but no obvious difference between the artificial reef and control areas is found. The similar seasonal and spacial distributions of net-phytoplankton community are also shown by the results according to the clusters, multidimensional scaling and similarity analysis. Therefore, the artificial reefs at present have no significant influence on community composition of net-phytoplankton. It could be speculated that (1) the total scale (only 230 concrete reefs with a total of 5000 air cubic meters) and settle time (since 2008) of artificial reefs in this area are still not large and long enough to reflect the ecological effects; (2) the control area is close to the reef area, and the sampling stations are near the islands, so the influences of current and island effect on phytoplankton may overwhelm the influence of reefs. Canonical correspondence analysis (CCA) showed that temperature, nutrition (DIN and PO₄-P), salinity and suspended solids were the main factors influencing net-phytoplankton community in turn.